Introduction: Disparities in breast cancer (BC) incidence and outcomes exist across racial/ethnic groups in the U.S. and by socioeconomic status (SES). The extent to which lower SES independently impacts breast cancer outcomes in different racial/ethnic groups is not fully described. Our purpose was to determine the impact of SES on cancer-specific mortality among women with metastatic breast cancer.

Method: We conducted a large, population-based retrospective cohort study of women ages 18+ years diagnosed with de novo metastatic breast cancer using the Surveillance, Epidemiology and End Results Census Tract-level SES and Rurality Database (2000-2015). SES was described using the Yost index, a validated time-dependent composite score that reflects SES based on several components including education and income, with the 1st quintile representing the lowest and 5th quintile being the highest SES. Information on demographic and clinical characteristics, including hormone receptor (HR) status, cancer treatment, survival and cause of death were collected from cancer registry data. We determined associations between SES and BC-specific mortality in Fine and Gray regression models. Multivariable adjusted subdistribution hazard ratios (SHR) and 95% confidence intervals (CI) were calculated accounting for competing risks of death. We determined associations between SES and BC mortality overall and calculated stratum specific SHR estimates by racial/ethnic groups and HR status.

Results: In an overall cohort of 33,976 women with de novo metastatic BC, the majority were non-Hispanic white (67%), 17% were Black, 0.4% were American Indian/Alaskan Native, 6% were Asian/Pacific Islander and 10% were Hispanic. Compared to women in the highest SES quintile, women in the lowest SES were more likely to be uninsured or on Medicaid (25% vs. 7%) and have HR-negative disease (24% vs. 18%) but were similar with respect to treatment with surgery, radiation and chemotherapy. Overall, metastatic BC patients in the lowest SES quintile had a significantly increased risk of BC mortality compared to the highest SES quintile (adjusted SHR 1.27, 95% CI 1.22-1.32); however, these impacts of SES differed across racial/ethnic groups and by HR status. Risk estimates for the association between low SES (1st quintile) and BC mortality were lower among HR-positive white women (SHR 1.19, 95% CI 1.12-1.26) and minimal among Asian/Pacific Islander women (SHR 1.05, 95% CI 0.88-1.25). The greatest increased risk was observed among HR-negative Black women (SHR 1.38, 95% CI 1.00-1.90) with metastatic BC.

Conclusion: Independent of race/ethnicity, lower SES is significantly associated with BC-specific mortality among women with de novo metastatic disease. However, when stratifying these effects by racial/ethnic groups and HR status, the impact of SES appears to be greater among Black women with HR-negative metastatic BC.

Citation Format: Hsiao- Ching Huang, Mary H. Smart, Huiwen Deng, Ashwini Zolekar, Colin C. Hubbard, Kent F. Hoskins, Naomi Y. Ko, Gregory S. Calip. Differences in impact of socioeconomic status on cancer: Specific survival in metastatic breast cancer by race/ethnicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 776.